Infrared spectroscopy medium-density

FT-IR spectroscopy has been used in the investigation of welding crosslinked polyethylene pipes [23]. Three types of crosslinking systems were used namely, peroxide (PEXa), silane (PEXb) and electron beam (PEXc). Scholten and co-workers [23] observed that only PEXa pipes have a satisfactory electrofusion quality. The strength of electrofusion welds of PEXb and PEXc pipes is not acceptable. The most likely explanation for the differences in weld quality is related to the adhesion theory and more specifically to differences in composition. Figure 5.6 shows the infrared spectra of medium density polyethylene (MDPE), PEXa, PEXb and PEXc. 

Finally, the oxidation of D-glucose at Pt-based electrocatalysts incorporated in polypyrrole [55,56] or in polyaniline [57] was also considered. The first work [55] was carried out in Pt-doped polypyrrole films in a neutral medium (phosphate buffer) in view of biosensor applications. Then the use of Pt-Pd catalysts dispersed in PPy led to higher current densities of glucose oxidation than on pure metal dispersed in PPy. This may be related to the decrease of catalytic poisoning (by adsorbed CO as shown by infrared reflectance spectroscopy [58]), due to the presence of Pd. 

When light traversing an optically dense medium approaches an interface with a more optically rare medium at an angle exceeding a critical value, Bent = sin (rerare/ dens), total internal reflection occurs and an evanescent wave of exponentially deca5ung intensity penetrates the rarer medium. This phenomenon is at the heart of certain spectroscopic methods used to probe biomolecules at interfaces (199). In total internal reflection fluorescence (TIRF) spectroscopy (200-202), the evanescent wave excites fluorescent probes attached to the biomolecules, and detection of the emission associated with their decay provides information on the density, composition, and conformation of adsorbed molecules. In fourier transform infrared attenuated total reflection (FTIR-ATIR) spectroscopy (203,204), the evanescent wave excites certain molecular vibrational degrees of freedom, and the detected loss in intensity due to these absorbances can provide quantitative data on density, composition, and conformation. 

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